R-T-B based permanent magnet

Abstract

An object of the present invention is to provide an R-T-B based permanent magnet showing high residual magnetic flux density Br and coercive force HcJ, and further showing the same also after heavy rare earth element is diffused along grain boundaries. Provided is an R-T-B based permanent magnet in which, R is a rare earth element, T is an element other than the rare earth element, B, C, O or N, and B is boron. T at least includes Fe, Cu, Co and Ga, and a total of R content is 28.0 to 30.2 mass %, Cu content is 0.04 to 0.50 mass %, Co content is 0.5 to 3.0 mass %, Ga content is 0.08 to 0.30 mass %, and B content is 0.85 to 0.95 mass %, relative to 100 mass % of a total mass of R, T and B.

The invention claimed is: 
     
       1. An R-T-B based permanent magnet comprising an R-T-B sintered body and optionally a coating material thereon containing a heavy rare earth element not subjected to grain boundary diffusion heat treatment wherein,
 R is a rare earth element, T is an element other than the rare earth element, B, C, O or N, and B is boron, 
 T at least includes Fe, Cu, Co and Ga, 
 wherein in the R-T-B sintered body, a total of R content is 28.0 to 30.2 mass %, Cu content is 0.04 to 0.50 mass %, Co content is 1.0 to 3.0 mass %, Ga content is 0.08 to 0.30 mass %, and B content is 0.85 to 0.95 mass %, relative to 100 mass % of a total mass of R, T and B, 
 the R-T-B sintered body further includes O, 
 O content is 350 ppm or more and 800 ppm or less, relative to a total mass of the R-T-B based permanent magnet, 
 an atomic ratio of 14B/(Fe+Co) is more than zero and 1.01 or less, 
 R optionally includes a heavy rare earth element which is at least one of Tb and Dy and in a total amount of 0.5 mass % or less when present, 
 the R-T-B sintered body has a potential index of from 1,635 or more to 1,673 and a squareness ratio of from 97% to 99.8%, wherein potential index is defined as PI=Br+25×HcJ×4π/2,000; Br is a magnitude of a residual magnetic flux density measured by mT unit and HcJ is a coercive force measured by kA/m unit, 
 wherein the R-T-B sintered body has the following properties when coated with the coating material and the coated R-T-B sintered body is heat treated to effect grain boundary diffusion of the heavy rare earth element such that a concentration of the heavy rare earth element is reduced from outside to inside: 
 the magnet has a potential index of from 1,745 to 1,781 and a squareness ratio of from 90% to 99.1%. 
 
     
     
       2. The R-T-B based permanent magnet according to  claim 1 , wherein
 the total of R content is 29.2 to 30.2 mass %. 
 
     
     
       3. The R-T-B based permanent magnet according to  claim 1 , wherein
 R at least includes Nd. 
 
     
     
       4. The R-T-B based permanent magnet according to  claim 1 , wherein
 R at least includes Pr and 
 Pr content is more than zero to 10.0 mass % or less. 
 
     
     
       5. The R-T-B based permanent magnet according to  claim 1 , wherein
 R at least includes Nd and Pr. 
 
     
     
       6. The R-T-B based permanent magnet according to  claim 1 , wherein
 T further includes Al and 
 Al content is 0.15 to 0.30 mass %. 
 
     
     
       7. The R-T-B based permanent magnet according to  claim 1 , wherein
 T further includes Zr and 
 Zr content is 0.10 to 0.30 mass %. 
 
     
     
       8. The R-T-B based permanent magnet according to  claim 1 , further including C and
 C content is 1100 ppm or less relative to a total mass of the R-T-B based permanent magnet. 
 
     
     
       9. The R-T-B based permanent magnet according to  claim 1 , further including N and
 N content is 1000 ppm or less relative to a total mass of the R-T-B based permanent magnet. 
 
     
     
       10. The R-T-B based permanent magnet according to  claim 1 , wherein an atomic ratio of TRE/B is 2.2 to 2.7, where TRE is the total of R content. 
     
     
       11. The R-T-B based permanent magnet according to  claim 1 , wherein the heavy rare earth element is present in the R-T-B sintered body. 
     
     
       12. The R-T-B based permanent magnet according to  claim 1 , wherein the heavy rare earth element is not present in the R-T-B sintered body. 
     
     
       13. The R-T-B based permanent magnet according to  claim 1 , wherein the Ga content is 0.10 mass % or more and 0.30 mass % or less. 
     
     
       14. An R-T-B based permanent magnet comprising an R-T-B sintered body, wherein,
 R is a rare earth element, T is an element other than the rare earth element, B, C, O or N, and B is boron, 
 T at least includes Fe, Cu, Co and Ga, 
 a total of R content is 28.0 to 30.2 mass %, Cu content is 0.04 to 0.50 mass %, Co content is 1.0 to 3.0 mass %, Ga content is 0.08 to 0.30 mass %, and B content is 0.85 to 0.95 mass %, relative to 100 mass % of a total mass of R, T and B, 
 the R-T-B based permanent magnet further includes O, 
 O content is 350 ppm or more and 800 ppm or less, relative to a total mass of the R-T-B based permanent magnet, 
 an atomic ratio of 14B/(Fe+Co) is more than zero and 1.01 or less, 
 R includes a heavy rare earth element which is at least one of Tb and Dy and in a total amount of no greater than 0.5 mass %, and 
 the magnet has a potential index of from 1,635 to 1,673 and a squareness ratio of from 97% to 99.8%, wherein the potential index is defined a PI=Br+25×HcJ×4π/2,000: Br ia a magnitude of a residual magnetic flux density measured by mT unit and HcJ is a coercive force measured by kA/m unit. 
 
     
     
       15. The R-T-B based permanent magnet according to  claim 14 , wherein
 the total of R content is 29.2 to 30.2 mass %. 
 
     
     
       16. The R-T-B based permanent magnet according to  claim 14 , wherein
 R at least includes Nd. 
 
     
     
       17. The R-T-B based permanent magnet according to  claim 14 , wherein
 R at least includes Pr and 
 Pr content is more than zero to 10.0 mass % or less. 
 
     
     
       18. The R-T-B based permanent magnet according to  claim 14 , wherein
 R at least includes Nd and Pr. 
 
     
     
       19. The R-T-B based permanent magnet according to  claim 14 , wherein
 T further includes Al and 
 Al content is 0.15 to 0.30 mass %. 
 
     
     
       20. The R-T-B based permanent magnet according to  claim 14 , wherein
 T further includes Zr and 
 Zr content is 0.10 to 0.30 mass %. 
 
     
     
       21. The R-T-B based permanent magnet according to  claim 14 , further including C and
 C content is 1100 ppm or less relative to a total mass of the R-T-B based permanent magnet. 
 
     
     
       22. The R-T-B based permanent magnet according to  claim 14 , further including N and
 N content is 1000 ppm or less relative to a total mass of the R-T-B based permanent magnet. 
 
     
     
       23. The R-T-B based permanent magnet according to  claim 14 , wherein an atomic ratio of TRE/B is 2.2 to 2.7, where TRE is the total of R content. 
     
     
       24. The R-T-B based permanent magnet according to  claim 14 , wherein the heavy rare earth element, prior to diffusion heat treatment, is present only as a coating on the R-T-B based permanent magnet. 
     
     
       25. The R-T-B based permanent magnet according to  claim 14 , wherein the heavy rare earth element, prior to diffusion heat treatment, is present both as a coating on the R-T-B based permanent magnet and uniformly present in the R-T-B based permanent magnet. 
     
     
       26. The R-T-B based permanent magnet according to  claim 14 , wherein the Ga content is 0.10 mass % or more and 0.30 mass % or less.